How to recover a hidden wallet in a different wallet than TREZOR?

If Trezor ceases to exist, you can recover your standard wallet in another wallet using the seed phrase. However, how could you recover a hidden wallet with a password without the Trezor interface?

Only if you know how the cryptographic salt is applied to the seed phrase.

Not true, there are many other wallets that support passphrase, Both HW and SW wallets. Trezor follows BIP39 standard.